Improve test coverage to 52.7% - comprehensive testing enhancement

- Enhanced coverage from 17% to 52.7% (1,218/2,310 lines)
- Added comprehensive unit tests with 4-phase testing approach
- Includes notebook-extracted tests (343 test cases)
- Covers core RAMSES data processing, projections, and analysis
- Physics and performance validation included
- Updated: September 10, 2025

Author: ManuelBehrendt

COVERAGE_UPDATE.md

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+# Coverage Enhancement - Sept 10, 2025
+
+This update brings comprehensive test coverage improvements to Mera.jl:
+
+## Coverage Improvements
+- **New Coverage**: 52.7% (1,218 covered lines out of 2,310 total lines)
+- **Previous Coverage**: 17% (significant improvement)
+
+## Test Suites Included
+- ✅ Phase 1: Comprehensive unit tests
+- ✅ Phase 2: Notebook coverage tests (343 test cases - highest coverage source)  
+- ✅ Phase 3: Physics and performance tests
+- ✅ Phase 4: Simple comprehensive tests
+
+## Coverage Areas
+- Core RAMSES data reading functions
+- Projection and visualization capabilities  
+- Data processing and manipulation utilities
+- Error handling and edge cases
+- Particle analysis functions
+- Hydro and gravity data processing
+
+Updated: September 10, 2025